1. Field of the Invention
This invention relates to spindle motor stop control devices, and more particularly to a device for stopping a spindle motor which rotates at high speed.
2. Background Art
In a conventional spindle motor stop control device, a frequency generator (FG) operating in association with the spindle motor is used to detect the motor speed. That is, the speed of the spindle motor is detected from the output of the frequency generator, so that, according to the speed of the spindle motor, a reverse torque braking force is applied to the spindle motor thereby to stop the latter. However, the conventional device is disadvantageous in that the frequency generator is expensive, and the use of the expensive frequency generator for only the stop control of the spindle motor is not economical.
To overcome this difficulty the following method has been employed: After reverse torque braking force is applied to the spindle motor, the speed of the latter is monitored, and the application of the reverse torque braking force is allowed to last for a predetermined period of time t from the time instant that the speed of the spindle motor is decreased to a predetermined value. This method in effective in the playing of a CAV (constant angular velocity) disc. However, it is not so effective in the playing of a CLV (constant linear velocity) disc. That is, in the case of a CLV disc, the speed of rotation of the spindle motor is changed as the pickup is moved radially of the disc, and therefore the predetermined period of time t described above is set according to the speed of rotation of the spindle motor provided when the pickup is moved to the middle point radially of the disc. Accordingly, when the pickup is located in the inner region of the disc, the period of time is not long enough; that is, the application of the reverse torque braking force is insufficient, and it is too long when the pickup is located in the outer region of the disc, so that it is impossible to suitably stop the spindle motor.